It has also been reported that tumour cells can inhibit cytotoxic T lymphocyte infiltration by producing immunosuppressive cytokines, such as vascular endothelial growth factor (VEGF), transforming growth factor–β (TGF—β), or IL—10, and by reducing IL—2, a cytokine that can maintain cytotoxic T lymphocyte function27. This evidence concerns the gene IL2 and neoplasm.